Flexible external gear, wave gear device, and robot joint device

Abstract

To provide a flexible external gear which can create a wave gear device which is less likely to cause reliability degradation, and to provide a wave gear device and a robot joint device.SOLUTION: The invention relates to a flexible external gear 3 of a wave gear device including a rigid internal gear, the flexible external gear 3, and a wave generator. The wave gear device deforms the flexible external gear in conjunction with rotation of a cam, causes part of external teeth 31 to engage with parts of internal teeth, and rotates the flexible external gear 3 relative to the rigid internal gear according to a tooth number difference between the flexible external gear and the rigid internal gear. In at least one of a first object portion Pt1 and a second object portion, in which a thickness t1 changes, of the flexible external gear 3, an object curve C1 contributing to the change of the thickness t1 on a cross section along a rotation axis Ax1 has a curvature radius which does not include discontinuous points.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure generally relates to a flexible external gear, a strain wave gearing device, and a joint device for a robot, and more particularly to a flexible external gear used in a strain wave gearing device, a strain wave gearing device, and a joint device for a robot. [Background technology]

[0002] Patent Document 1 discloses a flexible external gear in a strain wave gear device, in particular a small-sized cup-shaped flexible external gear.

[0003] The wave gear device includes an annular rigid internal gear, a cup-shaped flexible external gear concentrically arranged inside the internal gear, and a wave generator with an elliptical profile fitted inside the flexible external gear. The flexible external gear includes a flexible cylindrical body, an annular diaphragm extending radially inward from one end of the cylindrical body in the direction of the central axis, a disc-shaped rigid boss continuous with the inner peripheral edge of the diaphragm, and external teeth formed on the outer peripheral surface portion of the other end of the cylindrical body.

[0004] The cylindrical body portion of this flexible external gear, where the external teeth are formed, is bent into an elliptical shape by the wave generator, and the external teeth located at both ends of the ellipse in the long axis direction mesh with the internal teeth of the rigid internal gear. Since there is a difference in the number of teeth between the two gears of 2n (n is a positive integer), when the wave generator 4 is rotated by a rotary drive source such as a motor, the meshing positions of the two gears move circumferentially, and a relative rotation corresponding to the difference in the number of teeth is generated between the two gears. Generally, the rigid internal gear is fixed, and a significantly reduced rotation is output from the flexible external gear.

[0005] Here, the outer end face contour of the diaphragm of the cup-shaped flexible external gear is defined to include a first concave circular arc with a first radius R1 and a second concave circular arc with a second radius R2 that is continuous with the first concave circular arc. The second radius R2 of the second concave circular arc is larger than the first radius R1 of the first concave circular arc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-141856 Summary of the Invention [Problem to be solved by the invention]

[0007] However, with a flexible external gear having the above-described shape, the flexible external gear repeatedly undergoes elastic deformation, which can lead to stress concentration at the boundary between the first and second concave arcs, which have different radii, on the surface of the flexible external gear, especially after long-term use. As a result, damage (such as cracks or breaks) can occur originating from the surface of the flexible external gear, potentially affecting the reliability of the strain wave gearing. Furthermore, in order to keep the rate of change of radius small to avoid stress concentration, it is necessary to set many arcs with different radii on the outer end face contour of the diaphragm, which makes it difficult to control the shape of the flexible external gear.

[0008] The present disclosure has been made in view of the above-mentioned circumstances, and aims to provide a flexible external gear, a wave gear device, and a robot joint device that can realize a wave gear device that is less likely to experience a decrease in reliability. [Means for solving the problem]

[0009] A flexible external gear according to one aspect of the present disclosure is a flexible external gear of a strain wave gearing. The strain wave gearing includes a rigid internal gear, a flexible external gear, and a strain wave generator. The rigid internal gear is an annular component having internal teeth. The flexible external gear is an annular component having external teeth and disposed inside the rigid internal gear. The strain wave generator includes a non-circular cam that is driven to rotate about a rotation axis, and a bearing attached to the outside of the cam. The strain wave generator is disposed inside the flexible external gear and generates a deflection in the flexible external gear. The strain wave gearing deforms the flexible external gear as the cam rotates, meshing a portion of the external teeth with a portion of the internal teeth, and rotating the flexible external gear relative to the rigid internal gear in accordance with the difference in the number of teeth between the flexible external gear and the rigid internal gear. In at least one of the first and second target portions of the flexible external gear where the thickness changes, the target curve that contributes to the change in thickness in a cross section along the rotation axis has a radius of curvature that does not include discontinuous points.

[0010] A wave gear device according to one aspect of the present disclosure includes the flexible external gear, the rigid internal gear, and the wave generator.

[0011] A robot joint device according to one aspect of the present disclosure includes the strain wave gear device, a first member fixed to the rigid internal gear, and a second member fixed to the flexible external gear. [Effects of the Invention]

[0012] The present disclosure has the advantage of being able to provide a flexible external gear, a strain wave gear device, and a robot joint device that can realize a strain wave gear device that is less likely to experience a decrease in reliability. [Brief explanation of the drawings]

[0013] [Figure 1A] FIG. 1A is a cross-sectional view showing a schematic configuration of a strain wave gear device according to a first embodiment. [Figure 1B] FIG. 1B is an enlarged view of region Z1 of FIG. 1A. [Figure 2A]FIG. 2A is a schematic view of the strain wave gear device as viewed from the input side of the rotary shaft. [Figure 2B] FIG. 2B is an enlarged view of region Z1 of FIG. 2A. [Figure 3A] FIG. 3A is a schematic exploded perspective view of the strain wave gear device as viewed from the output side of the rotary shaft. [Figure 3B] FIG. 3B is a schematic exploded perspective view of the strain wave gear device as viewed from the input side of the rotary shaft. [Figure 4] FIG. 4 is a cross-sectional view showing a schematic configuration of an actuator including the above strain wave gear device. [Figure 5] FIG. 5 is a cross-sectional view showing a schematic configuration of a flexible external gear of the strain wave gear device. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of a first target portion of a flexible external gear of the strain wave gear device. [Figure 7] FIG. 7 shows the configuration of a first target portion of the flexible external gear of the strain wave gear device, and is a schematic enlarged view of region Z1 in FIG. [Figure 8] FIG. 8 is a schematic diagram showing an example of a procedure for drawing Bezier curves that define the shape of the main parts of the flexible external gear of the strain wave gearing. [Figure 9] FIG. 9 is a diagram showing the results of a simulation of stress acting on the first target portion when comparing the flexible external gear of the strain wave gear device with a comparative example. [Figure 10] FIG. 10 is a schematic diagram showing the configuration of a second target portion of the flexible external gear of the strain wave gear device. [Figure 11] FIG. 11 is a diagram showing the results of a simulation of stress acting on the second target portion when comparing the flexible external gear of the strain wave gearing device with a comparative example. [Figure 12] FIG. 12 is a cross-sectional view showing an example of a robot using the above strain wave gear device. DETAILED DESCRIPTION OF THE INVENTION

[0014] (Embodiment 1) (1) Overview An overview of the wave gear device 1 according to this embodiment will be described below with reference to Figures 1A to 5. All drawings referred to in this disclosure are schematic, and the ratios of size and thickness of each component in the drawings do not necessarily reflect the actual dimensional ratios. For example, the tooth shapes, dimensions, number of teeth, etc. of the internal teeth 21 and external teeth 31 in Figures 2A to 3B are merely shown schematically for the purpose of explanation, and are not intended to be limited to the shapes shown in the drawings.

[0015] The wave gearing 1 according to this embodiment is a gearing including a rigid internal gear 2, a flexible external gear 3, and a wave generator 4. In this wave gearing 1, an annular flexible external gear 3 is disposed inside the annular rigid internal gear 2, and the wave generator 4 is disposed inside the flexible external gear 3. The wave generator 4 bends the flexible external gear 3 into a non-circular shape, thereby partially meshing the external teeth 31 of the flexible external gear 3 with the internal teeth 21 of the rigid internal gear 2. When the wave generator 4 rotates, the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction of the rigid internal gear 2, and a relative rotation corresponding to the difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 is generated between the two gears (the rigid internal gear 2 and the flexible external gear 3). If the rigid internal gear 2 is fixed, the relative rotation of the two gears will cause the flexible external gear 3 to rotate. As a result, the flexible external gear 3 produces a rotational output that is reduced at a relatively high reduction ratio according to the difference in the number of teeth between the two gears.

[0016] The wave generator 4, which causes deflection in the flexible external gear 3, has a non-circular cam 41 that is driven to rotate about an input-side rotation axis Ax1 (see FIG. 1A ), and a bearing 42. The bearing 42 is disposed between an outer peripheral surface 411 of the cam 41 and an inner peripheral surface 301 of the flexible external gear 3. An inner ring 422 of the bearing 42 is fixed to the outer peripheral surface 411 of the cam 41, and the outer ring 421 of the bearing 42 is pressed by the cam 41 via ball-shaped rolling elements 423, causing elastic deformation. Here, the rolling of the rolling elements 423 allows the outer ring 421 to rotate relative to the inner ring 422. Therefore, when the non-circular cam 41 rotates, the rotation of the inner ring 422 is not transmitted to the outer ring 421, and a wave motion is generated in the external teeth 31 of the flexible external gear 3 that are pressed by the cam 41. As a result of the wave motion of the external teeth 31, the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction of the rigid internal gear 2 as described above, and relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2.

[0017] In short, in this type of strain wave gear device 1, the wave generator 4 having the bearing 42 deflects the flexible external gear 3, and power is transmitted by the meshing of the internal teeth 21 and the external teeth 31.

[0018] The flexible external gear 3 is also called a flex spline, and is an annular part having external teeth 31. In this embodiment, the flexible external gear 3 is a cup-shaped part made of a relatively thin elastic metal body (metal plate), as shown in FIG. 5. In other words, the flexible external gear 3 has flexibility due to its relatively small (thin) thickness. The flexible external gear 3 has a cup-shaped main body 32.

[0019] As will be described in more detail below, the flexible external gear 3 of the wave gear drive 1 according to this embodiment employs a configuration in which stress concentration is unlikely to occur in at least one of the first target location Pt1 and the second target location Pt2, where the thickness t1 of the flexible external gear 3 (main body 32) varies. In other words, the thickness t1 of the flexible external gear 3 is not uniform, but varies in the first target location Pt1 and the second target location Pt2, which are parts of the flexible external gear 3. The flexible external gear 3 employs a configuration in which stress concentration is unlikely to occur in the first target location Pt1 and / or the second target location Pt2.

[0020] According to this aspect, damage (cracks, breaks, etc.) originating from the surface of the flexible external gear 3 is less likely to occur, and the reliability of the wave gearing device is less likely to be affected. As a result, it is possible to provide a wave gearing device 1 that is less likely to experience a decline in reliability. Furthermore, the wave gearing device 1 according to this embodiment is less likely to experience a decline in reliability, especially during long-term use, which in turn leads to improved transmission efficiency, a longer lifespan, and higher performance of the wave gearing device 1.

[0021] 4, the wave gearing 1 according to this embodiment, together with a drive source 101 and an output unit 102, constitutes an actuator 100. In other words, the actuator 100 according to this embodiment includes the wave gearing 1, a drive source 101, and an output unit 102. The drive source 101 rotates the wave generator 4. The output unit 102 extracts the rotational force of either the rigid internal gear 2 or the flexible external gear 3 as an output.

[0022] 4, the strain wave gearing 1 according to this embodiment constitutes a robot joint device 130 together with a first member 131 and a second member 132. In other words, the robot joint device 130 according to this embodiment includes the strain wave gearing 1, a first member 131, and a second member 132. The first member 131 is fixed to the rigid internal gear 2. The second member 132 is fixed to the flexible external gear 3. As a result, relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2 in the strain wave gearing 1, and this causes relative rotation between the first member 131 and the second member 132 in the robot joint device 130.

[0023] The robot joint device 130 according to this embodiment has the advantage that the reliability of the strain wave gear device 1 is less likely to decrease.

[0024] (2) Definition In this disclosure, "annular" refers to a ring-like shape that forms an enclosed space (region) at least in plan view, and is not limited to a circular shape (annular) such as a perfect circle in plan view, but may also be, for example, an elliptical shape or a polygonal shape. Furthermore, even if a shape has a bottom 322, such as a cup-shaped flexible external gear 3, if its body 321 is annular, it is called an "annular" flexible external gear 3.

[0025] In this disclosure, "rigidity" refers to the property of an object to resist deformation when an external force is applied to the object and the object attempts to deform. In other words, an object with rigidity is less likely to deform when an external force is applied to it. In addition, in this disclosure, "flexibility" refers to the property of an object to elastically deform (bend) when an external force is applied to it. In other words, an object with flexibility is more likely to elastically deform when an external force is applied to it. Therefore, "rigidity" and "flexibility" have opposing meanings.

[0026] In particular, in this disclosure, the "rigidity" of the rigid internal gear 2 and the "flexibility" of the flexible external gear 3 are used in a relative sense. In other words, the "rigidity" of the rigid internal gear 2 means that the rigid internal gear 2 has a high rigidity, at least relatively compared to the flexible external gear 3, meaning that it is less likely to deform even when an external force is applied. Similarly, the "flexibility" of the flexible external gear 3 means that the flexible external gear 3 has a high flexibility, at least relatively compared to the rigid internal gear 2, meaning that it is more likely to elastically deform when an external force is applied.

[0027] Furthermore, in this disclosure, one side of the rotation axis Ax1 (the right side in FIG. 1A) may be referred to as the "input side," and the other side of the rotation axis Ax1 (the left side in FIG. 1A) may be referred to as the "output side." In other words, in the example of FIG. 1A, the flexible external gear 3 has an opening surface 35 on the "input side" of the rotation axis Ax1. However, the "input side" and "output side" are merely labels used for the purpose of explanation, and are not intended to limit the positional relationship between the input and output when viewed from the strain wave gear device 1.

[0028] In the present disclosure, the term "non-circular" refers to a shape that is not a perfect circle, and includes, for example, an elliptical shape and an oval shape. In this embodiment, as an example, the non-circular cam 41 of the wave generator 4 is elliptical. In other words, in this embodiment, the wave generator 4 bends the flexible external gear 3 into an elliptical shape.

[0029] In this disclosure, the term "elliptical shape" refers to a general shape in which a perfect circle is squashed and the intersection of its major and minor axes, which are perpendicular to each other, is located at the center. It is not limited to a mathematical "ellipse," which is a curved line formed by a set of points whose sum of distances from two fixed points on a plane is constant. In other words, the cam 41 in this embodiment may be a curved line formed by a set of points whose sum of distances from two fixed points on a plane is constant, like a mathematical "ellipse," or it may be an elliptical shape, such as an oval, rather than a mathematical "ellipse." As mentioned above, all drawings referenced in this disclosure are schematic, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios. For example, in FIG. 2A, the shape of the cam 41 of the wave generator 4 is depicted as a somewhat exaggerated ellipse, but this is not intended to limit the actual shape of the cam 41.

[0030] In this disclosure, the term "axis of rotation" refers to a virtual axis (straight line) that serves as the center of rotational motion of a rotating body. In other words, the axis of rotation Ax1 is a virtual axis that does not have a physical entity. The wave generator 4 performs rotational motion around the axis of rotation Ax1.

[0031] In this disclosure, "internal teeth" and "external teeth" do not refer to a single "tooth," but rather to a set (group) of multiple "teeth." In other words, the internal teeth 21 of the rigid internal gear 2 are made up of a set of multiple teeth formed on the inner circumferential surface of the rigid internal gear 2. Similarly, the external teeth 31 of the flexible external gear 3 are made up of a set of multiple teeth formed on the outer circumferential surface 303 (see FIG. 1A) of the flexible external gear 3.

[0032] In this disclosure, "parallel" refers to a case where two straight lines on a plane do not intersect no matter how far they are extended, that is, a case where the angle between the two is exactly 0 degrees (or 180 degrees), as well as a case where the angle between the two is within an error range of a few degrees (for example, less than 10 degrees) from 0 degrees. Similarly, in this disclosure, "orthogonal" refers to a case where the angle between the two is exactly 90 degrees, as well as a case where the angle between the two is within an error range of a few degrees (for example, less than 10 degrees) from 90 degrees.

[0033] (3) Composition Hereinafter, detailed configurations of the strain wave gear device 1, the actuator 100, and the robot joint device 130 according to this embodiment will be described with reference to FIGS. 1A to 4. FIG.

[0034] Fig. 1A is a cross-sectional view showing the schematic configuration of the strain wave gear device 1, and Fig. 1B is an enlarged view of region Z1 in Fig. 1A. Fig. 2A is a schematic view of the strain wave gear device 1 as viewed from the input side of the rotation axis Ax1 (the right side of Fig. 1A), and Fig. 2B is an enlarged view of region Z1 in Fig. 2A. Fig. 3A is a schematic exploded perspective view of the strain wave gear device 1 as viewed from the output side of the rotation axis Ax1 (the left side of Fig. 1A). Fig. 3B is a schematic exploded perspective view of the strain wave gear device 1 as viewed from the input side of the rotation axis Ax1. Fig. 4 is a cross-sectional view showing the schematic configuration of an actuator 100 and a robot joint device 130 that include the strain wave gear device 1.

[0035] (3.1) Strain wave gearing As described above, the wave gearing 1 according to this embodiment includes the rigid internal gear 2, the flexible external gear 3, and the wave generator 4. In this embodiment, the materials of the rigid internal gear 2, the flexible external gear 3, and the wave generator 4, which are components of the wave gearing 1, are metals such as stainless steel, cast iron, carbon steel for machine structures, chromium-molybdenum steel, phosphor bronze, or aluminum bronze. The metals referred to here include metals that have been subjected to surface treatments such as nitriding.

[0036] In addition, in this embodiment, a cup-type wave gearing device is exemplified as an example of the wave gearing device 1. That is, the wave gearing device 1 according to this embodiment uses a flexible external gear 3 formed in a cup shape. The wave generator 4 is combined with the flexible external gear 3 so as to be housed inside the cup-shaped flexible external gear 3.

[0037] In addition, in this embodiment, as an example, the strain wave gear device 1 is used with the rigid internal gear 2 fixed to an input side case 111 (see FIG. 4) and an output side case 112 (see FIG. 4), etc. As a result, relative rotation between the rigid internal gear 2 and the flexible external gear 3 causes the flexible external gear 3 to rotate relative to the fixed member (the input side case 111, etc.).

[0038] Furthermore, in this embodiment, when the wave gearing 1 is used in the actuator 100, a rotational force is applied as an input to the wave generator 4, and a rotational force is extracted as an output from the flexible external gear 3. In other words, the wave gearing 1 operates with the rotation of the wave generator 4 as the input rotation and the rotation of the flexible external gear 3 as the output rotation. As a result, the wave gearing 1 produces output rotation that is reduced at a relatively high reduction ratio relative to the input rotation.

[0039] Furthermore, in the wave gear device 1 according to this embodiment, the input-side rotation axis Ax1 and the output-side rotation axis Ax2 are on the same straight line. In other words, the input-side rotation axis Ax1 and the output-side rotation axis Ax2 are coaxial. Here, the input-side rotation axis Ax1 is the center of rotation of the wave generator 4 to which the input rotation is applied, and the output-side rotation axis Ax1 is the center of rotation of the flexible external gear 3 that generates the output rotation. In other words, in the wave gear device 1, output rotation is obtained that is reduced in speed at a relatively high reduction ratio relative to the input rotation on the same axis.

[0040] The rigid internal gear 2 is also called a circular spline, and is an annular component having internal teeth 21. In this embodiment, the rigid internal gear 2 has an annular shape, with at least the inner circumferential surface being a perfect circle in a plan view. The internal teeth 21 are formed on the inner circumferential surface of the annular rigid internal gear 2 along the circumferential direction of the rigid internal gear 2. The multiple teeth constituting the internal teeth 21 all have the same shape and are provided at equal pitch over the entire circumferential area of the inner circumferential surface of the rigid internal gear 2. In other words, the pitch circle of the internal teeth 21 is a perfect circle in a plan view. The rigid internal gear 2 has a predetermined thickness in the direction of the rotation axis Ax1. All of the internal teeth 21 are formed over the entire length of the rigid internal gear 2 in the thickness direction. All of the tooth traces of the internal teeth 21 are parallel to the rotation axis Ax1.

[0041] As described above, the rigid internal gear 2 is fixed to the input side case 111 (see FIG. 4) and the output side case 112 (see FIG. 4), etc. Therefore, the rigid internal gear 2 has a plurality of fixing holes 22 (see FIGS. 3A and 3B) for fixing.

[0042] The flexible external gear 3, also known as a flex spline, is an annular component having external teeth 31. In this embodiment, the flexible external gear 3 is a component formed into a cup shape using a relatively thin elastic metal body (metal plate). In other words, the flexible external gear 3 is flexible due to its relatively small (thin) thickness. The flexible external gear 3 has a cup-shaped main body 32. The main body 32 has a trunk 321 and a bottom 322. The trunk 321 has a cylindrical shape in which at least the inner circumferential surface 301 is a perfect circle in a plan view when no elastic deformation occurs in the flexible external gear 3. The central axis of the trunk 321 coincides with the rotation axis Ax1. The bottom 322 is disposed on one opening surface of the trunk 321 and has a disk shape that is a perfect circle in a plan view. The bottom 322 is disposed on the opening surface of the pair of opening surfaces of the trunk 321 that is on the output side of the rotation axis Ax1. As described above, the trunk 321 and the bottom 322 as a whole form the main body 32 in the form of a bottomed cylinder, i.e., a cup-like shape, that is open to the input side of the rotation axis Ax1. In other words, an opening surface 35 is formed on the end surface of the flexible external gear 3 opposite the bottom 322 in the direction of the rotation axis Ax1. In other words, the flexible external gear 3 is cylindrical, having the opening surface 35 on one side in the tooth trace direction D1 (here, on the input side of the rotation axis Ax1). In this embodiment, the trunk 321 and the bottom 322 are integrally formed from a single metal member, thereby realizing a seamless main body 32.

[0043] Here, the wave generator 4 is combined with the flexible external gear 3 such that the non-circular (elliptical) wave generator 4 is fitted inside the body portion 321. As a result, the flexible external gear 3 receives an external force from the wave generator 4 in the radial direction (direction perpendicular to the rotation axis Ax1) from the inside to the outside, and is elastically deformed into a non-circular shape. In this embodiment, by combining the wave generator 4 with the flexible external gear 3, the body portion 321 of the flexible external gear 3 is elastically deformed into an elliptical shape. In other words, a state in which no elastic deformation occurs in the flexible external gear 3 means a state in which the wave generator 4 is not combined with the flexible external gear 3. Conversely, a state in which elastic deformation occurs in the flexible external gear 3 means a state in which the wave generator 4 is combined with the flexible external gear 3.

[0044] More specifically, the wave generator 4 is fitted into the end of the inner circumferential surface 301 of the body portion 321 opposite to the bottom portion 322 (the input side of the rotation axis Ax1). In other words, the wave generator 4 is fitted into the end of the body portion 321 of the flexible external gear 3 on the opening surface 35 side in the direction of the rotation axis Ax1. Therefore, when elastic deformation occurs in the flexible external gear 3, the end of the flexible external gear 3 on the opening surface 35 side in the direction of the rotation axis Ax1 deforms more greatly than the end on the bottom portion 322 side, and becomes closer to an elliptical shape. Due to this difference in the amount of deformation in the direction of the rotation axis Ax1, when elastic deformation occurs in the flexible external gear 3, the inner circumferential surface 301 of the body portion 321 of the flexible external gear 3 includes a tapered surface that is inclined with respect to the rotation axis Ax1.

[0045] Furthermore, the external teeth 31 are formed along the circumferential direction of the body portion 321 on at least the end of the outer peripheral surface 303 (see FIG. 1A) of the body portion 321 opposite the bottom portion 322 (the input side of the rotation axis Ax1). In other words, the external teeth 31 are provided on at least the end of the body portion 321 on the opening surface 35 side in the direction of the rotation axis Ax1 of the flexible external gear 3. The multiple teeth constituting the external teeth 31 all have the same shape and are provided at an equal pitch over the entire circumferential area of the outer peripheral surface 303 of the flexible external gear 3. In other words, the pitch circle of the external teeth 31 is a perfect circle in a plan view when no elastic deformation occurs in the flexible external gear 3. The external teeth 31 are formed only within a range of a certain width from the edge of the body portion 321 on the opening surface 35 side (the input side of the rotation axis Ax1). Specifically, at least a portion of the body 321 where the wave generator 4 is fitted in the direction of the rotation axis Ax1 (the end portion on the opening surface 35 side) has external teeth 31 formed on the outer circumferential surface 303. The tooth traces of the external teeth 31 are all parallel to the rotation axis Ax1.

[0046] In short, in the wave gear device 1 according to this embodiment, the tooth traces of both the internal teeth 21 of the rigid internal gear 2 and the external teeth 31 of the flexible external gear 3 are parallel to the rotation axis Ax1. Therefore, in this embodiment, the "tooth trace direction D1" is a direction parallel to the rotation axis Ax1. The dimension of the tooth trace direction D1 of the internal teeth 21 is the face width of the internal teeth 21, and similarly, the dimension of the tooth trace direction D1 of the external teeth 31 is the face width of the external teeth 31, so the tooth trace direction D1 is synonymous with the face width direction.

[0047] In this embodiment, as described above, the rotation of the flexible external gear 3 is extracted as output rotation. For this reason, the output section 102 (see FIG. 4) of the actuator 100 is attached to the flexible external gear 3. A plurality of attachment holes 33 are formed in the bottom section 322 of the flexible external gear 3 for attaching a shaft serving as the output section 102. Furthermore, a through hole 34 is formed in the center of the bottom section 322. The area around the through hole 34 in the bottom section 322 is thicker than other parts of the bottom section 322.

[0048] The flexible external gear 3 configured in this manner is disposed inside the rigid internal gear 2. Here, the flexible external gear 3 is combined with the rigid internal gear 2 so that only the end of the outer circumferential surface 303 of the body portion 321 opposite the bottom portion 322 (the input side of the rotation axis Ax1) is inserted inside the rigid internal gear 2. In other words, the portion of the body portion 321 into which the wave generator 4 is fitted (the end on the opening surface 35 side) in the direction of the rotation axis Ax1 is inserted inside the rigid internal gear 2. Here, external teeth 31 are formed on the outer circumferential surface 303 of the flexible external gear 3, and internal teeth 21 are formed on the inner circumferential surface of the rigid internal gear 2. Therefore, when the flexible external gear 3 is disposed inside the rigid internal gear 2, the external teeth 31 and the internal teeth 21 face each other.

[0049] Here, the number of teeth of the internal teeth 21 of the rigid internal gear 2 is 2N (N is a positive integer) more than the number of teeth of the external teeth 31 of the flexible external gear 3. In this embodiment, as an example, N is "1", and the number of teeth (of the external teeth 31) of the flexible external gear 3 is "2" more than the number of teeth (of the internal teeth 21) of the rigid internal gear 2. This difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 defines the reduction ratio of the output rotation to the input rotation in the strain wave gear device 1.

[0050] 1A and 1B, as an example, in this embodiment, the relative positions of the flexible external gear 3 and the rigid internal gear 2 in the direction of the rotation axis Ax1 are set so that the centers of the external teeth 31 in the tooth trace direction D1 and the internal teeth 21 in the tooth trace direction D1 face each other. In other words, the centers of the external teeth 31 of the flexible external gear 3 and the internal teeth 21 of the rigid internal gear 2 in the tooth trace direction D1 are aligned at the same position in the direction of the rotation axis Ax1. In addition, in this embodiment, the dimension (tooth width) of the external teeth 31 in the tooth trace direction D1 is larger than the dimension (tooth width) of the internal teeth 21 in the tooth trace direction D1. Therefore, in the direction parallel to the rotation axis Ax1, the internal teeth 21 are contained within the range of the tooth trace of the external teeth 31. In other words, the external teeth 31 protrude in at least one direction in the tooth trace direction D1 relative to the internal teeth 21. In this embodiment, the external teeth 31 protrude relative to the internal teeth 21 in both directions of the tooth trace direction D1 (on the input side and output side of the rotation axis Ax1).

[0051] Here, when no elastic deformation occurs in the flexible external gear 3 (when the wave generator 4 is not combined with the flexible external gear 3), the pitch circle of the external teeth 31, which form a perfect circle, is set to be slightly smaller than the pitch circle of the internal teeth 21, which also form a perfect circle. In other words, when no elastic deformation occurs in the flexible external gear 3, the external teeth 31 and the internal teeth 21 face each other with a gap between them and do not mesh with each other.

[0052] On the other hand, when elastic deformation occurs in the flexible external gear 3 (when the wave generator 4 is combined with the flexible external gear 3), the body portion 321 bends into an elliptical shape (non-circular shape), so that the external teeth 31 of the flexible external gear 3 partially mesh with the internal teeth 21 of the rigid internal gear 2. In other words, the body portion 321 of the flexible external gear 3 (at least the end portion on the opening surface 35 side) elastically deforms into an elliptical shape, so that the external teeth 31 located at both ends in the major axis direction of the elliptical shape mesh with the internal teeth 21, as shown in FIG. 2A . In other words, the major axis of the pitch circle of the external teeth 31 that describe an ellipse matches the diameter of the pitch circle of the internal teeth 21 that describe a perfect circle, and the minor axis of the pitch circle of the external teeth 31 that describe an ellipse is smaller than the diameter of the pitch circle of the internal teeth 21 that describe a perfect circle. In this way, when the flexible external gear 3 elastically deforms, some of the teeth that make up the external teeth 31 mesh with some of the teeth that make up the internal teeth 21. As a result, in the wave gear device 1, it is possible to make some of the external teeth 31 mesh with some of the internal teeth 21.

[0053] The wave generator 4 is also called a wave generator, and is a component that causes deflection in the flexible external gear 3 to generate wave motion in the external teeth 31 of the flexible external gear 3. In this embodiment, the wave generator 4 is a component whose outer circumferential shape is non-circular, specifically elliptical, in plan view.

[0054] The wave generator 4 has a non-circular (here, elliptical) cam 41 and a bearing 42 attached to the outer periphery of the cam 41. That is, the non-circular (elliptical) cam 41 is fitted inside an inner ring 422 of the bearing 42, and the cam 41 is assembled to the bearing 42. As a result, the bearing 42 receives an external force from the cam 41 in the radial direction (a direction perpendicular to the rotation axis Ax1) from the inside to the outside of the inner ring 422, and is thereby elastically deformed into a non-circular shape. In other words, a state in which no elastic deformation occurs in the bearing 42 means a state in which the cam 41 is not assembled to the bearing 42. Conversely, a state in which elastic deformation occurs in the bearing 42 means a state in which the cam 41 is assembled to the bearing 42.

[0055] The cam 41 is a non-circular (here, elliptical) component that is driven to rotate around the rotation axis Ax1 on the input side. The cam 41 has an outer circumferential surface 411 (see FIG. 1B), and at least the outer circumferential surface 411 is made of a metal plate that is elliptical in plan view. The cam 41 has a predetermined thickness in the direction of the rotation axis Ax1 (i.e., the tooth trace direction D1). This gives the cam 41 approximately the same rigidity as the rigid internal gear 2. However, the thickness of the cam 41 is smaller (thinner) than the thickness of the rigid internal gear 2. In this embodiment, as described above, the rotation of the wave generator 4 is defined as the input rotation. Therefore, the input unit 103 (see FIG. 4) of the actuator 100 is attached to the wave generator 4. A cam hole 43 for attaching a shaft serving as the input unit 103 is formed in the center of the cam 41 of the wave generator 4.

[0056] The bearing 42 has an outer ring 421, an inner ring 422, and a plurality of rolling elements 423. In this embodiment, as an example, the bearing 42 is a deep groove ball bearing using spherical balls as the rolling elements 423.

[0057] The outer ring 421 and the inner ring 422 are both annular components. The outer ring 421 and the inner ring 422 are both annular components made of a relatively thin elastic metal body (metal plate). That is, the outer ring 421 and the inner ring 422 are flexible due to their relatively small (thin) thickness. In this embodiment, the outer ring 421 and the inner ring 422 each have an annular shape that is a perfect circle in a plan view when no elastic deformation occurs in the bearing 42 (when the cam 41 is not combined with the bearing 42). The inner ring 422 is one size smaller than the outer ring 421 and is disposed inside the outer ring 421. Here, the inner diameter of the outer ring 421 is larger than the outer diameter of the inner ring 422, so a gap is generated between the inner peripheral surface 425 of the outer ring 421 and the outer peripheral surface of the inner ring 422.

[0058] The plurality of rolling elements 423 are arranged in the gap between the outer ring 421 and the inner ring 422. The plurality of rolling elements 423 are arranged side by side in the circumferential direction of the outer ring 421. The plurality of rolling elements 423 are all metal balls of the same shape, and are provided at equal pitches over the entire circumferential area of the outer ring 421. Although not specifically shown here, the bearing 42 further has a cage, and the plurality of rolling elements 423 are held between the outer ring 421 and the inner ring 422 by the cage.

[0059] In the present embodiment, as an example, the dimensions of the outer ring 421 and the inner ring 422 in the width direction (the direction parallel to the rotation axis Ax1) are the same as the thickness of the cam 41. In other words, the dimensions of the outer ring 421 and the inner ring 422 in the width direction are smaller than the thickness of the rigid internal gear 2.

[0060] With this configuration of the bearing 42, when the cam 41 is assembled with the bearing 42, the inner ring 422 of the bearing 42 is fixed to the cam 41, and the inner ring 422 elastically deforms into an elliptical shape that follows the outer peripheral shape of the cam 41. At this time, the outer ring 421 of the bearing 42 is pressed by the inner ring 422 via the multiple rolling elements 423, and elastically deforms into an elliptical shape. Therefore, both the outer ring 421 and the inner ring 422 of the bearing 42 elastically deform into an elliptical shape. In this state where elastic deformation occurs in the bearing 42 (when the cam 41 is assembled with the bearing 42), the outer ring 421 and the inner ring 422 form elliptical shapes that are similar to each other.

[0061] Even when elastic deformation occurs in the bearing 42, the gap between the outer ring 421 and the inner ring 422 is maintained substantially constant around the entire circumference of the outer ring 421 due to the presence of multiple rolling elements 423 between the outer ring 421 and the inner ring 422. In this state, the multiple rolling elements 423 roll between the outer ring 421 and the inner ring 422, allowing the outer ring 421 to rotate relative to the inner ring 422. Therefore, when elastic deformation occurs in the bearing 42, if the cam 41 rotates about the rotation axis Ax1, the rotation of the cam 41 is not transmitted to the outer ring 421, but the elastic deformation of the inner ring 422 is transmitted to the outer ring 421 via the multiple rolling elements 423. In other words, in the wave generator 4, when the cam 41 rotates about the rotation axis Ax1, the outer ring 421 elastically deforms such that the major axis of the elliptical shape formed by the outer ring 421 rotates about the rotation axis Ax1. Therefore, as for the wave generator 4 as a whole, the outer peripheral shape of the elliptical wave generator 4 when viewed from the input side of the rotation axis Ax1 changes with the rotation of the cam 41 so that its major axis rotates around the rotation axis Ax1.

[0062] The wave generator 4 configured as above is disposed inside the flexible external gear 3. The flexible external gear 3 is assembled with the wave generator 4 so that only the end of the inner circumferential surface 301 of the body 321 opposite the bottom 322 (the opening surface 35 side) is fitted into the wave generator 4. In this case, the bearing 42 of the wave generator 4 is disposed between the outer circumferential surface 411 of the cam 41 and the inner circumferential surface 301 of the flexible external gear 3. The outer diameter of the outer ring 421 in a state where no elastic deformation occurs in the bearing 42 (a state where the cam 41 is not assembled with the bearing 42) is the same as the inner diameter of the flexible external gear 3 (body 321) in a state where no elastic deformation occurs. Therefore, the outer circumferential surface 424 (see FIG. 2B ) of the outer ring 421 of the wave generator 4 contacts the inner circumferential surface 301 of the flexible external gear 3 over the entire circumferential direction of the bearing 42. Therefore, when elastic deformation occurs in the flexible external gear 3 (when the wave generator 4 is combined with the flexible external gear 3), the body part 321 bends into an elliptical shape (non-circular shape). In this state, the flexible external gear 3 is fixed to the outer ring 421 of the bearing 42.

[0063] However, because the flexible external gear 3 and the wave generator 4 are merely fitted together, the flexible external gear 3 and the outer ring 421 of the bearing 42 are not completely fixed. Therefore, as described above, a small gap X1 (see FIG. 1B ) is generated between the flexible external gear 3 and the outer ring 421 fitted inside the flexible external gear 3. Strictly speaking, because the outer peripheral surface 424 of the outer ring 421 has a slightly smaller diameter than the inner peripheral surface 301 of the flexible external gear 3, the gap X1 between the outer ring 421 and the flexible external gear 3 is not completely filled, and at least a partial gap X1 is generated. Then, due to the influence of this gap X1, relative rotation can occur between the outer ring 421 and the flexible external gear 3 as the cam 41 of the wave generator 4 rotates and the outer ring 421 and the flexible external gear 3 elastically deform. This relative rotation is, for example, about one thousandth or one hundredth of the rotational speed of the cam 41, but such relative rotation causes the outer ring 421 and the flexible external gear 3 to rub against each other, which is one cause of fretting wear.

[0064] In this disclosure, the term "gap" refers to a space that can occur between the opposing surfaces of two objects, and a gap can occur between the two objects even if the two objects are not separated. In other words, even if the two objects are in contact, a small gap can occur between the two objects. Between the flexible external gear 3 and the outer ring 421 fitted inside the flexible external gear 3, a gap X1 occurs between the outer peripheral surface 424 of the outer ring 421 and the inner peripheral surface 301 of the flexible external gear 3, which face each other. However, since the outer peripheral surface 424 of the outer ring 421 and the inner peripheral surface 301 of the flexible external gear 3 basically come into contact with each other, no large gap X1 occurs between them. Therefore, the gap X1 between the outer ring 421 and the flexible external gear 3 is a small gap that can occur partially between the outer peripheral surface 424 of the outer ring 421 and the inner peripheral surface 301 of the flexible external gear 3. As an example, a microscopic gap X1 is generated between the outer peripheral surface 424 of the outer ring 421 and the inner peripheral surface 301 of the flexible external gear 3, which allows the lubricant Lb1 to penetrate.

[0065] 2A , in the wave gear device 1 configured as described above, the body portion 321 of the flexible external gear 3 bends into an elliptical shape (non-circular shape), causing the external teeth 31 of the flexible external gear 3 to partially mesh with the internal teeth 21 of the rigid internal gear 2. In other words, (the body portion 321 of) the flexible external gear 3 elastically deforms into an elliptical shape, causing the external teeth 31 at two locations corresponding to both ends of the elliptical shape in the major axis direction to mesh with the internal teeth 21. When the cam 41 rotates around the rotation axis Ax1, the rotation of the cam 41 is not transmitted to the outer ring 421 and the flexible external gear 3, but the elastic deformation of the inner ring 422 is transmitted to the outer ring 421 and the flexible external gear 3 via multiple rolling elements 423. Therefore, the outer peripheral shape of the flexible external gear 3, which is elliptical when viewed from the input side of the rotation axis Ax1, changes with the rotation of the cam 41 so that its major axis rotates around the rotation axis Ax1.

[0066] As a result, wave motion is generated in the external teeth 31 formed on the outer peripheral surface 303 of the flexible external gear 3. The generation of wave motion in the external teeth 31 causes the meshing positions between the internal teeth 21 and the external teeth 31 to move in the circumferential direction of the rigid internal gear 2, causing relative rotation between the flexible external gear 3 and the rigid internal gear 2. In other words, the external teeth 31 mesh with the internal teeth 21 at both ends in the major axis direction of the elliptical shape formed by (the body portion 321 of) the flexible external gear 3, and therefore, as the major axis of this elliptical shape rotates about the rotation axis Ax1, the meshing positions between the internal teeth 21 and the external teeth 31 move. In this way, the wave gear device 1 according to this embodiment deforms the flexible external gear 3 in conjunction with the rotation of the wave generator 4 about the rotation axis Ax1, meshing some of the external teeth 31 with some of the internal teeth 21, and rotating the flexible external gear 3 in accordance with the difference in the number of teeth with the rigid internal gear 2.

[0067] Incidentally, in the strain wave gearing 1, as described above, the difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 determines the reduction ratio of the output rotation to the input rotation in the strain wave gearing 1. In other words, if the number of teeth of the rigid internal gear 2 is "V1" and the number of teeth of the flexible external gear 3 is "V2," the reduction ratio R1 is expressed by the following formula 1.

[0068] R1=V2 / (V1-V2) (Equation 1) In other words, the smaller the difference in the number of teeth (V1-V2) between the rigid internal gear 2 and the flexible external gear 3, the larger the reduction ratio R1. As an example, if the number of teeth V1 of the rigid internal gear 2 is 72, the number of teeth V2 of the flexible external gear 3 is 70, and the difference in the number of teeth (V1-V2) is 2, then the reduction ratio R1 is 35 according to the above formula 1. In this case, when viewed from the input side of the rotation axis Ax1, when the cam 41 rotates clockwise around the rotation axis Ax1 through one revolution (360 degrees), the flexible external gear 3 rotates counterclockwise around the rotation axis Ax1 by the difference in the number of teeth of 2 (i.e., 10.3 degrees).

[0069] According to the strain wave gear device 1 of this embodiment, such a high reduction ratio R1 can be achieved with a combination of one gear stage (rigid internal gear 2 and flexible external gear 3).

[0070] Furthermore, the wave gear device 1 only needs to include at least a rigid internal gear 2, a flexible external gear 3, and a wave generator 4, and may further include, for example, a spline bush 113, etc., as described in the section "(3.2) Actuator."

[0071] Next, the tooth trace modification of the internal teeth 21 and the external teeth 31 in this embodiment will be described.

[0072] 1B, the internal teeth 21 have tooth roots 212 and tooth tips 213. Since the internal teeth 21 are provided on the inner peripheral surface of the rigid internal gear 2, the tooth roots 212 of the internal teeth 21 correspond to the inner peripheral surface of the rigid internal gear 2, and the tooth tips 213 protrude inward from the inner peripheral surface of the rigid internal gear 2 (toward the center of the rigid internal gear 2).

[0073] 1B, the external teeth 31 have tooth bottoms 312 and tooth tips 313. The external teeth 31 are provided on the outer peripheral surface 303 of (the body part 321 of) the flexible external gear 3, so the tooth bottoms 312 of the external teeth 31 correspond to the outer peripheral surface 303 of (the body part 321 of) the flexible external gear 3, and the tooth tips 313 protrude outward from the outer peripheral surface 303 of (the body part 321 of) the flexible external gear 3.

[0074] At the meshing position between the internal teeth 21 and the external teeth 31, the internal teeth 21 mesh with the external teeth 31 such that the tooth tips 313 of the external teeth 31 are inserted between a pair of adjacent tooth tips 213 of the internal teeth 21. At this time, the tooth bottoms 212 of the internal teeth 21 face the tooth tips 313 of the external teeth 31, and the tooth bottoms 312 of the external teeth 31 face the tooth tips 213 of the internal teeth 21. Ideally, a small gap is secured between the tooth bottoms 212 of the internal teeth 21 and the tooth tips 313 of the external teeth 31, and between the tooth bottoms 312 of the external teeth 31 and the tooth tips 213 of the internal teeth 21. In this state, the tooth surfaces of the internal teeth 21 and the external teeth 31 that face each other in the tooth thickness direction come into contact with each other, and power is transmitted between the rigid internal gear 2 and the flexible external gear 3.

[0075] Furthermore, the internal teeth 21 have chamfered portions 211 at both ends in the tooth trace direction D1. The chamfered portions 211 are C-faces that reduce the amount of protrusion of the internal teeth 21 on both sides in the tooth trace direction D1, and are portions that do not generally contribute to the meshing between the internal teeth 21 and the external teeth 31. In other words, the chamfered portions 211 of the internal teeth 21 do not contact the external teeth 31 even at the meshing positions between the internal teeth 21 and the external teeth 31. Similarly, the external teeth 31 have chamfered portions 311 at both ends in the tooth trace direction D1. The chamfered portions 311 are C-faces that reduce the amount of protrusion of the internal teeth 21 on both sides in the tooth trace direction D1, and are portions that do not generally contribute to the meshing between the internal teeth 21 and the external teeth 31. In other words, the chamfered portions 311 of the external teeth 31 do not contact the internal teeth 21 even at the meshing positions between the internal teeth 21 and the external teeth 31.

[0076] Here, in this embodiment, the internal teeth 21 of the rigid internal gear 2 have tooth trace modification portions 210. In other words, tooth trace modification is applied to at least the internal teeth 21 of the strain wave gearing 1. The tooth trace modification portions 210 of the internal teeth 21 are provided at least at one end in the tooth trace direction D1. In other words, the internal teeth 21 have tooth trace modification portions 210 at least at one end in the tooth trace direction D1 of the internal teeth 21. In this embodiment, the tooth trace modification portions 210 are provided at both ends of the internal teeth 21 in the tooth trace direction D1.

[0077] In this embodiment, the external teeth 31 of the flexible external gear 3 also have tooth lead modification portions 310. In other words, in the wave gearing 1, tooth lead modification is performed not only on the internal teeth 21 but also on the external teeth 31. The tooth lead modification portions 210 of the external teeth are provided on at least one end in the tooth lead direction D1. In other words, the external teeth 31 have tooth lead modification portions 310 on at least one end in the tooth lead direction D1 of the external teeth 31. In this embodiment, the tooth lead modification portions 310 are provided on both ends of the external teeth 31 in the tooth lead direction D1.

[0078] As described above, in the wave gearing 1 according to this embodiment, at least one of the internal teeth 21 and the external teeth 31 has the tooth lead modification portions 210, 310. The tooth lead modification portions 210, 310 make it possible to prevent stress concentration due to excessive tooth contact between the internal teeth 21 and the external teeth 31, and as a result, improve the tooth contact between the internal teeth 21 and the external teeth 31. This makes it difficult for foreign matter to be generated due to chipping or wear caused by contact between the internal teeth 21 and the external teeth 31, and makes it possible to realize a wave gearing 1 that is less susceptible to deterioration in reliability.

[0079] (3.2) Actuator Next, the configuration of the actuator 100 according to this embodiment will be described in more detail.

[0080] As shown in Fig. 4, the actuator 100 according to this embodiment includes the strain wave gearing 1 according to this embodiment, a drive source 101, and an output unit 102. That is, the actuator 100 includes the drive source 101 and the output unit 102 in addition to the rigid internal gear 2, flexible external gear 3, and wave generator 4 that constitute the strain wave gearing 1. In addition to the strain wave gearing 1, the drive source 101, and the output unit 102, the actuator 100 also includes an input unit 103, an input-side case 111, an output-side case 112, a spline bushing 113, a spacer 114, a first fastener 115, a second fastener 116, and a mounting plate 117. In this embodiment, the actuator 100 also includes input-side bearings 118 and 119, an input-side oil seal 120, output-side bearings 121 and 122, and an output-side oil seal 123.

[0081] In this embodiment, the materials of the parts of the actuator 100 other than the driving source 101, the input side oil seal 120, and the output side oil seal 123 are metals such as stainless steel, cast iron, carbon steel for mechanical structures, chromium molybdenum steel, phosphor bronze, or aluminum bronze.

[0082] The driving source 101 is a power generating source such as a motor (electric motor). The power generated by the driving source 101 is transmitted to the cam 41 of the wave generator 4 in the harm gearing 1. Specifically, the driving source 101 is connected to a shaft serving as an input unit 103, and the power generated by the driving source 101 is transmitted to the cam 41 via the input unit 103. This enables the driving source 101 to rotate the cam 41.

[0083] The output part 102 is a cylindrical shaft arranged along the rotation axis Ax2 on the output side. The central axis of the shaft serving as the output part 102 coincides with the rotation axis Ax2. The output part 102 is held by the output side case 112 so as to be rotatable about the rotation axis Ax2. The output part 102 is fixed to the bottom part 322 of the main body part 32 of the flexible external gear 3, and rotates together with the flexible external gear 3 about the rotation axis Ax2. In other words, the output part 102 extracts the rotational force of the flexible external gear 3 as an output.

[0084] The input unit 103 is a cylindrical shaft arranged along the input-side rotation axis Ax1. The central axis of the shaft serving as the input unit 103 coincides with the rotation axis Ax1. The input unit 103 is held by the input-side case 111 so as to be rotatable about the rotation axis Ax1. The input unit 103 is attached to the cam 41 of the wave generator 4 and rotates together with the cam 41 about the rotation axis Ax1. In other words, the input unit 103 transmits the power (rotational force) generated by the drive source 101 as an input to the cam 41. In this embodiment, as described above, the input-side rotation axis Ax1 and the output-side rotation axis Ax2 are on the same straight line, and therefore the input unit 103 and the output unit 102 are positioned on the same axis.

[0085] The input side case 111 holds the input part 103 via input side bearings 118 and 119 so that the input part 103 is rotatable. The pair of input side bearings 118 and 119 are arranged side by side with a gap between them along the rotation axis Ax1. In this embodiment, a shaft serving as the input part 103 penetrates the input side case 111, and the tip of the input part 103 protrudes from the input side end face of the input side case 111 on the rotation axis Ax1 (the right end face in FIG. 4 ). The gap between the input side end face of the input side case 111 on the input side of the rotation axis Ax1 and the input part 103 is sealed by an input side oil seal 120.

[0086] The output side case 112 holds the output part 102 via output side bearings 121 and 122 so that the output part 102 is rotatable. The pair of output side bearings 121 and 122 are arranged side by side with a gap between them along the rotation axis Ax2. In this embodiment, the shaft serving as the output part 102 penetrates the output side case 112, and the tip of the output part 102 protrudes from the end face of the output side of the rotation axis Ax1 in the output side of the output side case 112 (the left end face in FIG. 4 ). The gap between the output side end face of the output side of the rotation axis Ax1 of the output side case 112 and the output part 102 is sealed by an output side oil seal 123.

[0087] As shown in FIG. 4 , the input-side case 111 and the output-side case 112 are coupled to each other with the rigid internal gear 2 of the strain wave gearing 1 sandwiched between them in a direction parallel to the rotation axis Ax1, i.e., in the tooth trace direction D1. Specifically, the input-side case 111 contacts the rigid internal gear 2 from the input side of the rotation axis Ax1, and the output-side case 112 contacts the rigid internal gear 2 from the output side of the rotation axis Ax1. In this manner, the input-side case 111 is fastened to the output-side case 112 with screws (bolts) passing through the multiple fixing holes 22, with the rigid internal gear 2 sandwiched between them. As a result, the input-side case 111, the output-side case 112, and the rigid internal gear 2 are coupled to each other and integrated. In other words, the rigid internal gear 2, together with the input-side case 111 and the output-side case 112, constitute the outer shell of the actuator 100.

[0088] The spline bushing 113 is a cylindrical component for connecting the shaft serving as the input portion 103 to the cam 41. The spline bushing 113 is inserted into a cam hole 43 formed in the cam 41, and the shaft serving as the input portion 103 is inserted into the spline bushing 113 so as to pass through the spline bushing 113. Here, movement of the spline bushing 113 relative to both the cam 41 and the input portion 103 in the rotational direction about the rotation axis Ax1 is restricted, but the spline bushing 113 is movable at least relative to the input portion 103 in a direction parallel to the rotation axis Ax1. This achieves a spline connection structure as a connection structure between the input portion 103 and the cam 41. Therefore, the cam 41 is movable along the rotation axis Ax1 relative to the input portion 103 and rotates together with the input portion 103 about the rotation axis Ax1.

[0089] The spacer 114 is a component that fills the gap between the spline bushing 113 and the cam 41. The first fastener 115 is a component that prevents the spline bushing 113 from coming off the cam 41. The first fastener 115 is made of, for example, an E-ring, and is attached to the spline bushing 113 at a position on the input side of the rotation axis Ax1 when viewed from the cam 41. The second fastener 116 is a component that prevents the input portion 103 from coming off the spline bushing 113. The second fastener 116 is made of, for example, an E-ring, and is attached to the input portion 103 so as to come into contact with the spline bushing 113 from the output side of the rotation axis Ax1.

[0090] The mounting plate 117 is a component for mounting the shaft serving as the output portion 102 to the bottom portion 322 of the flexible external gear 3. Specifically, the mounting plate 117 is fastened to the flange portion with screws (bolts) passing through the multiple mounting holes 33, with the area around the through-hole 34 in the bottom portion 322 sandwiched between the mounting plate 117 and the flange portion of the output portion 102. In this way, the shaft serving as the output portion 102 is fixed to the bottom portion 322 of the flexible external gear 3.

[0091] In this embodiment, a lubricant Lb1 is enclosed inside the outer shell of the actuator 100, which is made up of the input side case 111, the output side case 112, and the rigid internal gear 2. In other words, a "lubricant reservoir" capable of storing liquid or gel-like lubricant Lb1 is present in the space surrounded by the input side case 111, the output side case 112, and the rigid internal gear 2.

[0092] That is, in the wave gear device 1 according to this embodiment, for example, a liquid or gel-like lubricant Lb1 is injected into the meshing portions between the internal teeth 21 and the external teeth 31, and between the outer ring 421 and the inner ring 422 of the bearing 42, etc. As an example, the lubricant Lb1 is liquid lubricating oil. When the wave gear device 1 is in use, the lubricant Lb1 also enters the gap X1 between the outer ring 421 (outer peripheral surface 424) of the bearing 42 and the flexible external gear 3.

[0093] As an example, in this embodiment, as shown in Fig. 4, the lubricant Lb1 is stored only in the lower part (vertical lower part) of the outer casing of the actuator 100 so that the liquid level of the lubricant Lb1 is located further below the lower ends of the output-side bearings 121, 122. Therefore, in the state shown in Fig. 4, only a portion of the external teeth 31 and the outer ring 421 of the bearing 42, etc. in the rotational direction is immersed in the lubricant Lb1. From this state, when the output part 102 rotates in conjunction with the rotation of the input part 103, the outer ring 421 and the flexible external gear 3 also rotate around the rotation axis Ax1. As a result, the entire external teeth 31 and the outer ring 421 of the bearing 42, etc. in the rotational direction are immersed in the lubricant Lb1.

[0094] (3.3) Robot joint device Next, the configuration of the robot joint device 130 according to this embodiment will be described in more detail.

[0095] 4, the robot joint device 130 according to this embodiment includes the strain wave gear device 1 according to this embodiment, a first member 131, and a second member 132. In other words, the robot joint device 130 includes the first member 131 and the second member 132 in addition to the rigid internal gear 2, flexible external gear 3, and wave generator 4 that constitute the strain wave gear device 1.

[0096] The first member 131 is a member fixed to the rigid internal gear 2, and the second member 132 is a member fixed to the flexible external gear 3. Therefore, in the strain wave gearing 1, relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2, which also causes relative rotation between the first member 131 and the second member 132. In this way, the robot joint device 130 forms a connecting portion when two or more members (the first member 131 and the second member 132) are connected (movably connected) via the strain wave gearing 1 in a state where they can move relative to each other.

[0097] Here, the first member 131 and the second member 132 may be directly or indirectly fixed to the rigid internal gear 2 and the flexible external gear 3, respectively. In the example of Fig. 4, the first member 131 is coupled to the output side case 112, and thereby indirectly coupled (fixed) to the rigid internal gear 2. Similarly, the second member 132 is coupled to the output section 102, and thereby indirectly coupled (fixed) to the flexible external gear 3.

[0098] In the robot joint device 130 configured in this manner, for example, when the cam 41 of the wave generator 4 rotates due to power generated by the drive source 101, relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2. Then, as the flexible external gear 3 rotates relative to the rigid internal gear 2, relative rotation occurs between the first member 131 and the second member 132 about the output-side rotation axis Ax2 (coaxial with the input-side rotation axis Ax1). As a result, the robot joint device 130 can drive the first member 131 and the second member 132, which are connected via the strain wave gear device 1, to rotate relatively about the rotation axis Ax1. This makes it possible for the robot joint device 130 to realize various robot joint mechanisms.

[0099] (4) Detailed structure of the flexible external gear Next, the configuration of the flexible external gear 3 of the strain wave gear device 1 according to this embodiment will be described in more detail with reference to FIGS.

[0100] (4.1) Overall structure of flexible external gear As described above, the flexible external gear 3 of the wave gear device 1 according to this embodiment has a main body 32 made of a relatively thin elastic metal body (metal plate) and formed in a cylindrical (cup-like) shape with an opening 35 on one side in the tooth trace direction D1 (here, on the input side of the rotation axis Ax1). As shown in Fig. 5, the main body 32 has a cylindrical trunk portion 321 and a disk-shaped bottom portion 322.

[0101] External teeth 31 are formed on the outer peripheral surface 303 of the body 321 at the end on the opening surface 35 side (the input side of the rotation axis Ax1). A circular through-hole 34 is formed in the center of the bottom 322, penetrating the bottom 322 along the rotation axis Ax1, and the area around the through-hole 34 in the bottom 322 forms a boss 36 that is thicker than other parts of the bottom 322. The boss 36 has an annular shape centered on the center of the bottom 322 (the rotation axis Ax1). The boss 36 is sufficiently thicker than parts of the bottom 322 other than the boss 36, and has sufficient rigidity to secure the output section 102. The boss 36 is formed with a plurality of mounting holes 33 (see FIG. 3A ) that each penetrate the boss 36 (bottom 322) along the rotation axis Ax1.

[0102] With this configuration, the flexible external gear 3 is fixed to the output part 102 with the boss 36 around the through hole 34 in the bottom part 322 sandwiched between the mounting plate 117 and the flange part of the output part 102 (see FIG. 4). That is, by tightening screws (bolts) through the multiple mounting holes 33 provided in the boss 36, the boss 36 is fixed in a sandwiched state between the mounting plate 117 and the flange part of the output part 102. In this way, the shaft serving as the output part 102 is fixed to the boss 36 on the bottom part 322 of the flexible external gear 3.

[0103] Incidentally, the thickness t1 of the main body 32 (body 321 and bottom 322) of the flexible external gear 3, excluding the external teeth 31 and boss 36, is set to be small (thin) enough to provide sufficient flexibility for the flexible external gear 3.

[0104] As shown in Fig. 5, when the surface facing outward of the cup-shaped flexible external gear 3 is defined as the outer surface S1 and the surface facing inward is defined as the inner surface S2, the thickness t1 here is determined by the distance between the outer surface S1 and the inner surface S2. The outer surface S1 includes the outer peripheral surface 303 of the body portion 321 and the surface of the bottom portion 322 facing the output side of the rotation axis Ax1 (left side in Fig. 5). The inner surface S2 includes the inner peripheral surface 301 of the body portion 321 and the surface of the bottom portion 322 facing the input side of the rotation axis Ax1 (right side in Fig. 5).

[0105] However, the thickness t1 of the flexible external gear 3 (excluding the external teeth 31 and the boss 36) is not uniform throughout, but varies partially. As shown in Fig. 5, the flexible external gear 3 according to this embodiment has a first target portion Pt1 and a second target portion Pt2, each of which has a varying thickness t1.

[0106] The first target portion Pt1 is a portion of the bottom portion 322 that includes the boundary between the boss 36 and a portion other than the boss 36 (the periphery of the boss 36). The bottom portion 322 is configured such that the thickness t1 in the first target portion Pt1 increases (gradually increases) as it approaches the boss 36. In this embodiment, the thickness t1, which is the distance from the inner surface S2 of the first target portion Pt1, is continuously changed by making the outer surface S1 a curved surface. The portion of the bottom portion 322 other than the boss 36 (the periphery of the boss 36) forms a tapered surface in which the outer surface S1 is inclined with respect to the inner surface S2 so that the thickness t1 gradually increases toward the center (the boss 36 side). The inner peripheral edge of the tapered surface is continuous with the boss 36 via the curved outer surface S1 of the first target portion Pt1.

[0107] The second target portion Pt2 is a portion of the trunk portion 321 that includes the end portion on the bottom portion 322 side (the output side of the rotation axis Ax1). The trunk portion 321 is configured so that the thickness t1 is partially reduced (thin-walled) at least in the second target portion Pt2. In this embodiment, the outer surface S1 of the second target portion Pt2 is curved, thereby continuously changing the thickness t1, which is the distance from the inner surface S2.

[0108] In this way, the flexible external gear 3 has the first target portion Pt1 and the second target portion Pt2 where the thickness t1 changes, and thus can achieve at a high level the shape change (elastic deformation) required of the flexible external gear 3. As a result, the wave generator 4 causes the flexible external gear 3 to deflect, making it easier to generate wave motion in the external teeth 31 of the flexible external gear 3, and a highly efficient wave gearing 1 can be realized.

[0109] As a comparative example of this type of flexible external gear 3, it is conceivable that the cross section (contour) of the outer surface S1 (curved surface) in the first target portion Pt1 (or the second target portion Pt2) is defined to include a first concave circular arc with a first radius R1 and a second concave circular arc with a second radius R2 (>R1) that is continuous with the first concave circular arc. A configuration formed by combining two arcs with different radii like this is also called a "two-stage circular arc."

[0110] However, in the comparative example described above, the flexible external gear 3 repeatedly undergoes elastic deformation, and especially after long-term use, stress may concentrate at the boundary between the first and second concave arcs, which have different radii, on the surface of the flexible external gear 3. As a result, damage (cracks, fractures, etc.) may occur originating from the surface of the flexible external gear 3, which may affect the reliability of the strain wave gear device 1.

[0111] As an example, if damage (such as cracks or fissures) originating on the surface of the flexible external gear 3 inhibits the deformation followability of the flexible external gear 3, excess energy will be required to rotate the wave generator 4, leading to reduced power transmission efficiency or a shortened lifespan due to increased load on the bearings 42. In other words, such damage leads to deterioration in the quality and characteristics of the wave gearing 1, which ultimately leads to a decrease in the reliability of the wave gearing 1. Furthermore, in order to keep the rate of change of radius small to avoid stress concentration, it is necessary to set many arcs with different radii in the cross section (contour) of the outer surface S1, which makes it difficult to control the shape of the flexible external gear 3.

[0112] By adopting the configuration described below, the flexible external gear 3 according to this embodiment can realize a strain wave gearing 1 that is less susceptible to a decrease in reliability compared to the comparative example that adopts such a "two-stage arc." Moreover, since there is no need to set many arcs with different radii in the cross section (contour) of the outer surface S1, as in the comparative example, it is less difficult to manage the shape of the flexible external gear 3 according to this embodiment.

[0113] That is, the wave gearing 1 according to this embodiment includes an annular rigid internal gear 2 having internal teeth 21, an annular flexible external gear 3 having external teeth 31, and a wave generator 4. The flexible external gear 3 is disposed inside the rigid internal gear 2. The wave generator 4 is disposed inside the flexible external gear 3 and causes deflection in the flexible external gear 3. The wave generator 4 has a non-circular cam 41 that is driven to rotate about the rotation axis Ax1, and a bearing 42 attached to the outside of the cam 41. The wave gearing 1 deforms the flexible external gear 3 as the cam 41 rotates, meshing some of the external teeth 31 with some of the internal teeth 21, and rotating the flexible external gear 3 relative to the rigid internal gear 2 in accordance with the difference in the number of teeth between the rigid internal gear 2 and the flexible external gear 3. Here, in the flexible external gear 3 of the wave gear device 1 according to this embodiment, in at least one of the first target portion Pt1 and the second target portion Pt2 of the flexible external gear 3 where the thickness t1 changes, the target curves C1, C2 (see Figures 6 and 10) that contribute to the change in thickness t1 in the cross section along the rotation axis Ax1 have a radius of curvature that does not include a discontinuity point.

[0114] According to this aspect, in at least one of the first target portion Pt1 and the second target portion Pt2 of the flexible external gear 3 where the thickness t1 changes, the target curves C1 and C2 that contribute to the change in thickness t1 are smooth curves that do not have inflection points where the radius of curvature changes. Therefore, in the flexible external gear 3 according to this embodiment, stress concentration is less likely to occur in at least one of the first target portion Pt1 and the second target portion Pt2, compared to the configuration in the comparative example where stress concentration can occur at the boundary between the first concave arc and the second concave arc, which have different radii. As a result, it is possible to realize a wave gearing device 1 that is less likely to suffer damage (such as cracks or breaks) originating from the surface of the flexible external gear 3 and is less likely to experience a decrease in reliability. Furthermore, the wave gearing device 1 according to this embodiment is less likely to experience a decrease in reliability, especially during long-term use, which ultimately leads to improved transmission efficiency, a longer life, and higher performance of the wave gearing device 1. Moreover, unlike the comparative example, there is no need to set many arcs with different radii in the cross section (contour) of the outer surface S1, so that in the flexible external gear 3 according to this embodiment, it is less difficult to manage its shape.

[0115] In this embodiment, as an example, the target curves C1 and C2 in both the first target portion Pt1 and the second target portion Pt2 have radii of curvature that do not include discontinuities. Below, the details of the target curves C1 and C2 will be explained, particularly using the target curve C1 in the first target portion Pt1 as an example, but unless otherwise specified, the target curve C2 in the second target portion Pt2 has a similar configuration.

[0116] That is, as shown in FIG. 6, in the first target region Pt1, the target curve C1, which is the outline (the contour line of the outer surface S1) in a cross section along the rotation axis Ax1, contributes to the change in thickness t1. The target curve C1 defines the three-dimensional shape of the curved surface serving as the outer surface S1 in the first target region Pt1. The target curve C1 is a curved line that is convex toward the rotation axis Ax1 so that the thickness t1 gradually increases toward the boss 36. In FIG. 6, a schematic enlarged view of the first target region Pt1 is shown in a speech bubble.

[0117] In this embodiment, the radius of curvature of the target curve C1 changes continuously over the entire length of the target curve C1. As a result, the target curve C1 has a radius of curvature that does not include any discontinuous points over its entire length. In other words, the target curve C1 does not have a constant radius of curvature over its entire length; rather, although the radius of curvature varies from section to section, it does not have any inflection points (discontinuous points) where the radius of curvature switches, and the radius of curvature changes smoothly over its entire length. This has the advantage of making it less likely for stress to concentrate at the boundaries of the radius of curvature.

[0118] Here, the target curve C1 is expressed by a function. That is, unlike the comparative example described above, the target curve C1 is not defined by multiple arcs with different radii, but is defined by a certain function. Therefore, unlike the comparative example, there is no need to set many arcs with different radii in the cross section (contour) of the outer surface S1, and therefore, in the flexible external gear 3 according to this embodiment, it is less difficult to manage its shape.

[0119] In this embodiment, as an example, the "function" defining the object curve C1 is a Bezier curve. That is, the object curve C1 is represented by a Bezier curve. In this disclosure, a "Bezier curve" is an N-1-th degree curve obtained from N control points. For example, quadratic Bezier curves or cubic Bezier curves are used to draw smooth curves on a computer. In this embodiment, by designing the object curve C1 using such a Bezier curve, it is possible to relatively easily determine the parameters of the object curve C1 that define the three-dimensional shape of the curved surface serving as the outer surface S1.

[0120] The target curve C1 defined by a Bezier curve in this way is a smooth curve without discontinuities in the radius of curvature, compared to the target curve C10 of the comparative example consisting of a two-stage circular arc, as shown in FIG.

[0121] Fig. 7 is an explanatory diagram conceptually showing an example of creating an object curve C1 defined by a Bezier curve. As shown in the lower part of Fig. 7, the object curve C1 is defined by a pair of endpoints P0 and P3, which are both ends of the object curve C1, and a pair of control points P1 and P2. That is, the object curve C1 made up of a Bezier curve is expressed by the following formula 1 using a variable t that varies in the range from "0" to "1" (t∈[0,1]).

number

[0122] As shown in the lower part of FIG. 7, if the horizontal axis (axis parallel to the rotation axis Ax1) is the X axis and the vertical axis (axis perpendicular to the rotation axis Ax1) is the Y axis, and the coordinate positions (X, Y) of P0, P1, P2, and P3 are defined as (X0, Y0), (X1, Y1), (X2, Y2), and (X3, Y3), respectively, the coordinate positions (X, Y) of the points that describe the target curve C1 can be expressed by the following equations 2 and 3.

number

Number

[0123] Figure 8 schematically shows the drawing procedure of a cubic Bézier curve defined by a pair of end points P0, P3 and a pair of control points P1, P2. That is, in order to obtain the coordinates of a point at the position of the ratio of t (0 < t < 1) from the end point P0 of the Bézier curve, the following calculation may be performed.

[0124] First, find points P4, P5, P6 that divide the three line segments P0 - P1, P1 - P2, P2 - P3 obtained by connecting the control points in order at the ratio of "t:1 - t". Next, find points P7, P8 that divide the two line segments P4 - P5, P5 - P6 obtained by connecting these points P4, P5, P6 in order at the ratio of "t:1 - t". Finally, find a point P9 that divides the line segment P7 - P8 connecting these two points P7, P8 at the ratio of "t:1 - t", and this point P9 becomes a point on the Bézier curve. By repeating this operation in the range of 0 < t < 1, a cubic Bézier curve with P0, P1, P2, P3 as control points can be obtained.

[0125] Figure 9 shows the results of simulating the stress applied to each first target part Pt1 by comparing a comparative example having a target curve C10 of a two - stage arc and a flexible external gear 3 according to the present embodiment having a target curve C1 composed of a Bézier curve. The flexible external gear 3 according to the present embodiment has a stress reduction of 9.3% from 904 MPa to 820 MPa at the stress concentration location in the first target part Pt1 compared to the comparative example.

[0126] Thus, in the flexible external gear 3 according to the present embodiment, by devising the shape of the target curve C1 in the first target part Pt1, stress concentration in the first target part Pt1 is less likely to occur. As a result, it is possible to realize a harmonic drive device 1 in which damage (such as cracks or fractures) starting from the surface of the flexible external gear 3 is less likely to occur and a decrease in reliability is less likely to occur.

[0127] Furthermore, as shown in FIG. 10, in the second target region Pt2, the target curve C2, which is the outline (the contour line of the outer surface S1) in a cross section along the rotation axis Ax1, contributes to the change in thickness t1. The target curve C2 defines the three-dimensional shape of the curved surface serving as the outer surface S1 in the second target region Pt2. The target curve C2 is a curved line that is convex toward the rotation axis Ax1 so that the thickness t1 gradually decreases toward the center of the second target region Pt2 in a direction parallel to the rotation axis Ax1. In FIG. 10, a schematic enlarged view of the second target region Pt2 is shown in a speech bubble.

[0128] In this embodiment, the radius of curvature of the object curve C2 also changes continuously over the entire length of the object curve C2, similar to the object curve C1. The object curve C2 is represented by a Bézier curve. As shown in FIG. 10, the object curve C2 defined by the Bézier curve in this way is a smooth curve with no discontinuities in the radius of curvature, compared to the object curve C20 of the comparative example, which is made up of two circular arcs.

[0129] 11 shows the results of simulating the stress applied to the second target region Pt2 of a comparative example having a two-stage circular arc symmetric curve C20 and a flexible external gear 3 according to this embodiment having a symmetric curve C2 consisting of a Bézier curve. Compared to the comparative example, the flexible external gear 3 according to this embodiment reduces the stress at the stress concentration point in the second target region Pt2 by 4.9%, from 470 MPa to 447 MPa.

[0130] In this way, in the flexible external gear 3 according to this embodiment, by devising the shape of the target curve C2 in the second target portion Pt2, stress concentration in the second target portion Pt2 is less likely to occur. As a result, it is possible to realize a strain wave gearing 1 in which damage (cracks, breaks, etc.) originating from the surface of the flexible external gear 3 is less likely to occur and reliability is less likely to decrease.

[0131] (5) Application examples Next, an application example of the strain wave gear device 1, the actuator 100, and the robot joint device 130 according to this embodiment will be described with reference to FIG.

[0132] 12 is a cross-sectional view showing an example of a robot 9 using the strain wave gear device 1 according to this embodiment. This robot 9 is a horizontally articulated robot, a so-called SCARA (Selective Compliance Assembly Robot Arm) type robot.

[0133] As shown in FIG. 12, the robot 9 includes two robot joint devices 130 (including the strain wave gear device 1) and a link 91. The two robot joint devices 130 are provided at two joint portions of the robot 9, respectively. The link 91 connects the two robot joint devices 130. In the example of FIG. 12, the strain wave gear device 1 is a top hat type strain wave gear device rather than a cup type strain wave gear device. In other words, the strain wave gear device 1 illustrated in FIG. 12 uses a flexible external gear 3 formed in a top hat shape.

[0134] (6) Variations Embodiment 1 is merely one of various embodiments of the present disclosure. Various modifications of Embodiment 1 are possible depending on the design, etc., as long as the object of the present disclosure can be achieved. Furthermore, all drawings referred to in this disclosure are schematic diagrams, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios. Modifications of Embodiment 1 are listed below. The modifications described below can be applied in appropriate combinations.

[0135] In the first embodiment, the target curves C1 and C2 have radii of curvature that do not include discontinuities in both the first target portion Pt1 and the second target portion Pt2, but it is sufficient that the target curves C1 and C2 have radii of curvature that do not include discontinuities in at least one of the first target portion Pt1 and the second target portion Pt2. That is, of the first target portion Pt1 and the second target portion Pt2, the target curve C1 may have a radius of curvature that does not include discontinuities only in the first target portion Pt1, or the target curve C2 may have a radius of curvature that does not include discontinuities only in the second target portion Pt2.

[0136] Furthermore, it is not necessary for the radii of curvature of the object curves C1, C2 to change continuously over the entire length of the object curves C1, C2. For example, the radii of curvature of the object curves C1, C2 may be the same over the entire length of the object curves C1, C2. In this case, the object curves C1, C2 have a uniform radius of curvature rather than varying depending on the portion as in a Bézier curve. Even with this configuration, the flexible external gear 3 is less likely to experience stress concentration in at least one of the first object portion Pt1 and the second object portion Pt2, compared to the configuration in the comparative example described above in which stress concentration can occur at the boundary between the first concave arc and the second concave arc, which have different radii.

[0137] Furthermore, it is not essential for the wave gear device 1 that the internal teeth 21 and the external teeth 31 are modified in tooth profile. For example, at least one of the internal teeth 21 and the external teeth 31 does not have to be modified in tooth profile.

[0138] Furthermore, the fact that each rolling element 423 is supported at four points in the bearing 42 is not an essential configuration for the strain wave gear device 1; for example, each rolling element 423 may be supported at two points.

[0139] Furthermore, the strain wave gearing 1 is not limited to the cup type described in the first embodiment, and may be, for example, a top hat type, a ring type, a differential type, a flat type (pancake type), or a shield type. For example, even a top hat type strain wave gearing 1 as shown in FIG. 12 has a cylindrical flexible external gear 3 that has an opening surface 35 on one side in the tooth trace direction D1, just like a cup type. In other words, the top hat type flexible external gear 3 has a flange portion on one end on the rotation axis Ax1 side and an opening surface 35 on the end opposite the flange portion. Even the top hat type flexible external gear 3 has external teeth 31 on the opening surface 35 side, and a wave generator 4 is fitted into the end.

[0140] Furthermore, the configuration of the actuator 100 is not limited to the configuration described in the first embodiment and can be modified as appropriate. For example, the connection structure between the input portion 103 and the cam 41 is not limited to a spline connection structure, and an Oldham coupling or the like may be used. By using an Oldham coupling as the connection structure between the input portion 103 and the cam 41, misalignment between the input-side rotation axis Ax1 and the wave generator 4 (cam 41) can be offset, and further, misalignment between the rigid internal gear 2 and the flexible external gear 3 can be offset. Furthermore, the cam 41 does not have to be movable along the rotation axis Ax1 relative to the input portion 103.

[0141] Furthermore, application examples of the strain wave gearing 1, actuator 100, and robot joint device 130 according to this embodiment are not limited to the horizontal articulated robot described above, but may also be, for example, industrial robots other than horizontal articulated robots, or non-industrial robots. Examples of industrial robots other than horizontal articulated robots include vertical articulated robots and parallel link robots. Examples of non-industrial robots include domestic robots, nursing care robots, and medical robots.

[0142] Furthermore, bearing 42 is not limited to a deep groove ball bearing, but may be, for example, an angular contact ball bearing. Furthermore, bearing 42 is not limited to a ball bearing, but may be, for example, a roller bearing, such as a cylindrical roller bearing, a needle roller bearing, or a tapered roller bearing, in which rolling elements 423 are made of "rollers" that are not ball-shaped. Even if rolling elements 423 are not ball-shaped (spherical), a pressure difference occurs when rolling elements 423 roll, and rolling elements 423 function as a pump structure.

[0143] Furthermore, the material of each component of the strain wave gear device 1, the actuator 100, or the robot joint device 130 is not limited to metal, but may be, for example, a resin such as engineering plastic.

[0144] Furthermore, the lubricant Lb1 is not limited to a liquid substance such as lubricating oil (oil), but may be a gel substance such as grease.

[0145] (summary) As described above, the flexible external gear (3) according to the first aspect is the flexible external gear (3) of the strain wave gearing (1), and the strain wave gearing (1) includes the rigid internal gear (2), the flexible external gear (3), and the wave generator (4). The rigid internal gear (2) is an annular component having internal teeth (21). The flexible external gear (3) is an annular component having external teeth (31) and disposed inside the rigid internal gear (2). The wave generator (4) includes a non-circular cam (41) that is driven to rotate about the rotation axis (Ax1), and a bearing (42) that is attached to the outside of the cam (41). The wave generator (4) is disposed inside the flexible external gear (3) and generates a deflection in the flexible external gear (3). The strain wave gearing (1) deforms the flexible external gear (3) in accordance with the rotation of the cam (41), meshing some of the external teeth (31) with some of the internal teeth (21), and rotating the flexible external gear (3) relative to the rigid internal gear (2) in accordance with the difference in the number of teeth between the flexible external gear (3) and the rigid internal gear (2). In at least one of a first target portion (Pt1) and a second target portion (Pt2) of the flexible external gear (3) where the thickness (t1) changes, symmetric curves (C1, C2) that contribute to the change in the thickness (t1) in a cross section along the rotation axis (Ax1) have radii of curvature that do not include discontinuous points.

[0146] According to this aspect, in at least one of the first target portion (Pt1) and the second target portion (Pt2) of the flexible external gear (3) where the thickness (t1) changes, the target curves (C1, C2) that contribute to the change in thickness (t1) are smooth curves that do not have inflection points where the radius of curvature changes. Therefore, in the flexible external gear (3), stress concentration is less likely to occur in at least one of the first target portion (Pt1) and the second target portion (Pt2) compared to a configuration in which stress concentration may occur at the boundary between the first concave arc and the second concave arc, which have different radii. As a result, it is possible to realize a strain wave gearing device (1) that is less likely to suffer damage (such as cracks or breaks) originating from the surface of the flexible external gear (3) and is less likely to experience a decrease in reliability.

[0147] In the flexible external gear (3) according to the second aspect, in the first aspect, the radius of curvature of the symmetric curves (C1, C2) changes continuously over the entire length of the symmetric curves (C1, C2).

[0148] According to this embodiment, the radius of curvature of the target curves (C1, C2) is not constant over the entire length, but differs from part to part, but does not have any inflection points (discontinuous points) where the radius of curvature changes, and the radius of curvature changes smoothly over the entire length. Therefore, there is an advantage that stress concentration at the boundary of the radius of curvature is unlikely to occur.

[0149] In the flexible external gear (3) according to the third aspect, in the second aspect, the symmetry curves (C1, C2) are expressed by functions.

[0150] According to this embodiment, there is no need to set many arcs with different radii in the cross section (contour), so that control of the shape of the flexible external gear (3) is less likely to become difficult.

[0151] In the flexible external gear (3) according to the fourth aspect, the symmetric curves (C1, C2) in the third aspect are expressed by Bezier curves.

[0152] According to this embodiment, the parameters of the target curves (C1, C2) can be determined relatively easily.

[0153] In the flexible external gear (3) according to the fifth aspect, in the first aspect, the radii of curvature of the symmetric curves (C1, C2) are the same over the entire length of the symmetric curves (C1, C2).

[0154] According to this embodiment, the parameters of the target curves (C1, C2) can be determined relatively easily.

[0155] A wave gear device (1) according to a sixth aspect includes a flexible external gear (3) according to any one of the first to fifth aspects, a rigid internal gear (2), and a wave generator (4).

[0156] According to this embodiment, it is possible to realize a strain wave gearing device (1) in which damage (cracks, breaks, etc.) originating from the surface of the flexible external gear (3) is unlikely to occur and in which deterioration in reliability is unlikely to occur.

[0157] A robot joint device (130) according to the seventh aspect includes a wave gear device (1) according to the sixth aspect, a first member (131) fixed to a rigid internal gear (2), and a second member (132) fixed to a flexible external gear (3).

[0158] According to this aspect, it is possible to provide a robot joint device (130) that is less susceptible to damage (cracks, breaks, etc.) originating from the surface of the flexible external gear (3) and is less susceptible to deterioration in reliability.

[0159] The configurations according to the second to fifth aspects are not essential for the flexible external gear (3) and can be omitted as appropriate. [Explanation of symbols]

[0160] 1 Strain wave gearing 2 Rigid internal gear 3 Flexible external gear 4. Wave Generator 21 Inner teeth 31 Outer teeth 41 Cam 42 bearings 130 Robot joint device 131 First member 132 Second member Ax1 Rotation axis C1, C2 target curve Pt1 First target area Pt2 Second target area t1 thickness

Claims

1. an annular rigid internal gear having internal teeth; an annular flexible external gear having external teeth and disposed inside the rigid internal gear; a wave generator that has a non-circular cam that is driven to rotate around a rotation axis and a bearing attached to the outside of the cam, and is disposed inside the flexible external gear and causes deflection in the flexible external gear, The flexible external gear of a strain wave gear device is configured to deform the flexible external gear in accordance with the rotation of the cam, mesh some of the external teeth with some of the internal teeth, and rotate the flexible external gear relative to the rigid internal gear in accordance with a difference in the number of teeth between the flexible external gear and the rigid internal gear, In at least one of a first target portion and a second target portion of the flexible external gear, where the thickness changes, a target curve that contributes to the change in thickness in a cross section along the rotation axis has a radius of curvature that does not include a discontinuous point. Flexible external gear.

2. the radius of curvature of the target curve varies continuously over the entire length of the target curve; The flexible external gear according to claim 1 .

3. The target curve is represented by a function: The flexible external gear according to claim 2 .

4. The target curve is represented by a Bezier curve. The flexible external gear according to claim 3 .

5. The radius of curvature of the target curve is the same along the entire length of the target curve. The flexible external gear according to claim 1 .

6. A flexible external gear according to any one of claims 1 to 5, the rigid internal gear; The wave generator, Wave gearing.

7. The strain wave gear device according to claim 6; a first member fixed to the rigid internal gear; and a second member fixed to the flexible external gear. Robotic joint device.

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